Conventional tires to be mounted on four-wheel drive vehicles and light trucks need to be excellent in off-road running performance. In order to secure the off-road running performance, these tires employ a tread pattern formed primarily of a block pattern with a large number of edge portions. However, since such a tire having a block pattern has a tread contact area smaller than that of a tire having a rib pattern, the following problem arises. When the tire having a block pattern runs on general road surfaces, uneven wear called heel-and-toe wear is likely to occur in the surfaces of the blocks. In particular, in a case where lateral grooves of a large width are formed in such a tire in order to secure the performance of running on a muddy ground, uneven wear becomes more likely to occur. At the same time, since the block stiffness is reduced, the driving stability at the time of running on general road surfaces is deteriorated.
For the purpose of securing both on- and off-road running performances, the following proposal has heretofore been made. In this proposal, a projecting platform portion extending from the groove bottom is formed on a groove-wall surface in each tire circumferential groove (see, for example, Patent Document 1). However, in this proposal, the edge portions, in the circumferential direction, of each block is cut out over the entire length thereof, in the circumferential direction, by the formation of the platform portion. Accordingly the following problems arise. Since the block stiffness is reduced, the driving stability at the time of running on general road surfaces is deteriorated. In addition, an insufficient width of each block leads to a deterioration in the performance (particularly, the traction performance) at the time of running on a muddy ground.
Patent Document 1: Japanese Patent Application Kokai Publication No. Hei 9-300915